Ranges from in situ tumors, to invasive tumors, and to metastatic disease. It can present as a nonhealing wound, often attributed to trauma by the patient. Types include SCC in situ (Bowen disease), invasive SCC, and metastatic (or aggressive) SCC. In situ tumors are typically thin, flesh-colored to erythematous, scaly plaques, while invasive SCC may present as an exophytic tumor or ulcer.
[Figure caption and citation for the preceding image starts]:
Squamous cell carcinoma on the ear with surrounding actinic damage
From the collection of Dr Jessica M. Sheehan and Dr Keyoumars Soltani [Citation ends].
Tumors may be friable and bleed easily and are located mostly on sun-exposed areas of skin, such as the head and neck (84%) and extensor upper extremities (13%).
[7]Rundel RD. Promotional effects of ultraviolet radiation on human basal and squamous cell carcinoma. Photochem Photobiol. 1983;38:569-575.
http://www.ncbi.nlm.nih.gov/pubmed/6647566?tool=bestpractice.com

Once the diagnosis of primary cutaneous malignant melanoma is established, the standard of care is complete excision of the malignancy with an appropriate margin depending on the Breslow depth. The goals of treatment are to remove the primary tumor and to prevent persistent disease, local recurrence, and, ultimately, metastatic disease. Metastases are treated depending on the site (nodal, in-transit, or systemic).

A low-grade vasoformative neoplasm associated with human herpesvirus-8 (HHV-8) or Kaposi sarcoma herpesvirus (KSHV) infection.
[20]Chang Y, Cesarman E, Pessin MS, et al. Identification of herpesvirus-like DNA sequences in AIDS-associated Kaposi's sarcoma. Science. 1994;266:1865-1869.
http://www.ncbi.nlm.nih.gov/pubmed/7997879?tool=bestpractice.com
[Figure caption and citation for the preceding image starts]:
Kaposi sarcoma cutaneous purple-brown plaque on the foot
From the collection of Dr Bruce J. Dezube [Citation ends].
Lesions frequently involve mucocutaneous sites, but may become more extensive to involve the lymph nodes and visceral organs. Skin lesions evolve from an early patch, to a plaque, and later to ulcerating tumor nodules. There are 4 main subtypes: epidemic AIDS-associated, classic sporadic, iatrogenic and transplant-associated, and African endemic Kaposi sarcoma. In HIV-positive people, highly active antiretroviral therapy (HAART) without treatment interruptions may help prevent Kaposi sarcoma or result in a less-aggressive presentation. AIDS patients with Kaposi sarcoma should adhere to an effective, uninterrupted antiretroviral regimen in order to avoid disease progression and/or the development of new lesions. Non-nucleoside reverse transcriptase inhibitor (NNRTI)-based regimens are as effective as protease inhibitor (PI)-based regimens in terms of their protection.
[21]Portsmouth S, Stebbing J, Gill J, et al. A comparison of regimens based on non-nucleoside reverse transcriptase inhibitors or protease inhibitors in preventing Kaposi's sarcoma. AIDS. 2003;17:F17-F22.
http://journals.lww.com/aidsonline/Fulltext/2003/07250/A_comparison_of_regimens_based_on_non_nucleoside.1.aspx
http://www.ncbi.nlm.nih.gov/pubmed/12853764?tool=bestpractice.com

Therapy is given for symptom palliation, to prevent disease progression, and for cosmetic reasons. Treatment is individualized according to prognosis and the desired outcome of therapy. Treatment options are similar for each of the epidemiologic forms of Kaposi sarcoma, but may need to be tailored according to drug availability in resource-poor settings. Supportive care may be necessary in severely ill patients.

Heterogeneous group of uncommon disorders characterized by clonal accumulation of T lymphocytes primarily or exclusively in the skin. Mycosis fungoides and its leukemic variant, Sézary syndrome, are the most common subtypes. Establishing a diagnosis is often difficult, as the disease can manifest in a number of different ways, including flat patches, raised plaques, large tumors, and/or marked erythroderma (intense and widespread reddening of the skin).
[Figure caption and citation for the preceding image starts]:
Cutaneous T-cell lymphoma: extensive patch disease
From the collection of the Christie NHS Foundation Trust, Manchester, UK; used with permission [Citation ends].
Diagnosis is based on clinical findings, skin biopsy, and laboratory blood tests, and usually requires specialist expertise. Early-stage disease is usually managed with skin-directed therapy (topical medications, phototherapy, and localized radiation therapy). If skin disease is extensive or refractory, or the patient presents with advanced disease, systemic therapies are often necessary (chemotherapy, biologic or immunologic therapy, photopheresis). Clinical trials may be considered in early and advanced disease if the patient is a suitable candidate. The choice of skin-directed therapy or systemic treatment is usually dependent on both doctor and patient preference, as no one treatment option has been shown to be superior to another.

Lesions are skin-colored, yellowish or erythematous, ill-defined, irregularly shaped, small scaly macules or plaques localized in sun-exposed areas of the body (e.g., face, lower lip, dorsum of the hands, forearms, bald areas of the scalp, and ears).
[Figure caption and citation for the preceding image starts]:
Regular actinic keratosis
From the collection of the Department of Dermatology and Cutaneous Surgery, University of Miami Miller School of Medicine [Citation ends].
Typically, they occur in middle-aged or older men with light-colored skin and a history of chronic sun exposure. Has the potential to progress into an invasive squamous cell carcinoma (SCC). The risk of progression to SCC has been calculated to be between 0.025% and 16% per year.
[22]Marks R, Rennie G, Selwood TS. Malignant transformation of solar keratoses to squamous cell carcinoma. Lancet. 1988;1:795-797.
http://www.ncbi.nlm.nih.gov/pubmed/2895318?tool=bestpractice.com
[23]Glogau RG. The risk of progression to invasive disease. J Am Acad Dermatol. 2000;42:23-24.
http://www.ncbi.nlm.nih.gov/pubmed/10607353?tool=bestpractice.com
Although diagnosed clinically, a biopsy may help to rule out SCC.

As it is very difficult to predict which AK lesion might progress to squamous cell carcinoma (SCC), the recommendation is to treat all AKs.
[24]Werner RN, Stockfleth E, Connolly SM, et al; International League of Dermatological Societies, European Dermatology Forum. Evidence- and consensus-based (S3) guidelines for the treatment of actinic keratosis - short version. J Eur Acad Dermatol Venereol. 2015;29:2069-2079.
http://onlinelibrary.wiley.com/doi/10.1111/jdv.13180/full
http://www.ncbi.nlm.nih.gov/pubmed/26370093?tool=bestpractice.com
Treatment options should be chosen depending on variables such as number, size, anatomic location, change in growth pattern, and prior treatment of the lesions. The goal of the treatment is the total destruction of the AKs, to minimize the risk of progression to invasive SCC, while obtaining the best cosmetically acceptable outcome. Treatment consists of destructive methods (e.g., cryotherapy with liquid nitrogen, curettage with or without electrodesiccation, chemical peels, and photodynamic therapy) or topical medication (e.g., topical fluorouracil, imiquimod, diclofenac, or ingenol mebutate). In addition, all patients are advised to wear broad-spectrum sunscreen regardless of treatment.

Sunburn is an acute inflammatory reaction of the skin induced by overexposure to UV radiation. Skin findings include erythema and edema, with or without vesiculation, followed by desquamation. Symptoms include pain and/or pruritus. Acute sunburn is a self-limited condition and typically requires only supportive care. Primary prevention via sun avoidance, physical protection, and the appropriate use of sunscreen is key to managing the condition, as cellular damage caused by UV radiation is irreversible and may with time increase the risk of skin cancer. No current treatments can reverse UV-induced DNA damage in the skin.
[25]Han A, Maibach HI. Management of acute sunburn. Am J Clin Dermatol. 2004;5:39-47.
http://www.ncbi.nlm.nih.gov/pubmed/14979742?tool=bestpractice.com